As everyone else has noted, Chimay is pretty easy to find. Now, if you are looking for extremely rare and interesting beers, the Best Damn Beer Shop (inside Super Junior's Market on 7th between C and Broadway) always impresses me with the beer selection. I tend to think of myself as a beer geek, and I usually find stuff I have never even heard of, and Sid (who runs the place) is extremely knowledgeable. However, no matter what Sid suggests, avoid the sour stout: its just wrong.